Power conservation is a growing issue in circuitry as the recent trend towards more energy efficient data center design has become an important issue within Information Technology (IT) industry. One area of concern in power conservation has been the change of modes (e.g., from normal to sleep and vice versa) of circuits. Specifically, a subsystem level stand-by (sleep mode) design has been available, but the current circuit design method does not allow for circuit level control of the stand-by operation. Moreover, fast switching between the sleep and normal modes is essential to enable efficient power usage in digital systems. Current methods of sleeping and wake-up are conducted as a long-term static policy.